The present invention relates generally to the field of medical equipment for the diagnosis of ailments, and in particular to a new and useful apparatus and method for helping with the diagnosis of lung diseases.
The Signal and Speech Research Group (SRG) of Rensselaer Polytechnic Institute (RPI) has carried out research on algorithms for signal processing and their application since 1981. The group has been led by Professor Michael Savic, the inventor of the present application. Since 1985 the SRG has focused on high-risk, innovative research in all aspects of signal processing. Current areas include speaker recognition, language identification, detection of cholesterol deposits in blood vessels, speech recognition, automatic pipeline leak detection, voice character transformation, speaker separation (the cocktail party problem) and others.
Patents have been awarded for some of this work to RPI and Professor Savic, including: U.S. Pat. No. 7,024,360 for System for reconstruction of symbols in a sequence; U.S. Pat. No. 5,675,506 for Detection of leaks in vessels; U.S. Pat. No. 5,623,421 for Monitoring pressurized vessels for leaks, ruptures or hard hits; U.S. Pat. No. 5,416,724 for Detection of leaks in pipelines; and U.S. Pat. No. 5,327,893 for Detection of cholesterol deposits in arteries. These patents are all incorporated here by reference.
Chest auscultation, that is, the act of listening for sounds made by the lungs to aid in the diagnosis of certain disorders, is an effective, nonintrusive and inexpensive way to assess the condition of a patient's lungs. Many clinicians use chest auscultation in a cursory manner because they are not skilled in recognizing certain lung sounds.
A brief explanation of this technique can be found in an article at URL: http://www.leedsth.nhs.uk/sites/emibank/clinicians/nursing/documents/auscul ta.pdf, entitled “Chest Auscultation,” by Bob McMaster, February/2001.
The training of doctors for this technique is long and difficult. Moreover, the human ear is sensitive to a certain sound frequency range only (e.g. 15 to 20,000 Hz) and some significant lung sounds are not in this range and therefore will not be heard, even by the most highly trained practitioner.
To better understand the present invention, a brief description of breath sounds and of what is under investigation is necessary. Many distinctive sounds are generated by a diseased lung. These may be roughly grouped into two broad categories, the adventitious sounds and the abnormally transmitted sounds. See, for example, Lehrer, S., “Understanding Lung Sounds”, W.B. Saunders Company, 1993. Sounds like crackles, wheezes and pleural friction rubs are included in the adventitious sounds group while sounds like egophony, pectoriloque, bronchophony, bronchial breathing and abnormally diminished breath sounds are included in the abnormally transmitted sounds group. Recent scientific investigations, aided by advances in acoustics and electronics, provide insights into the mechanism of production of these sounds.
Diseases that are explored here are identifiable in the adventitious breath sounds and especially in crackles. Crackles are short, explosive, nonmusical sounds that can be described as to quantity (scanty or profuse) and timing (inspiratory or expiratory, early or late). Two commonly accepted theories suggest that crackles can be produced by the bubbling of air through airway secretions or by sudden opening of small airways (see: Wilkins, L. R. at al, “Lung Sounds: A practical guide”, Mosby-Yaer Book, Inc., 1996). Crackles associated with the movement of airways secretions in larger airways are typically coarse and may occur during both inspiration and expiration. They may clear with suctioning of effective coughing. Crackles associated with the sudden opening of airways may be produced by a rapid equalization of pressure between open and collapsed airways (see: Ploysongsang, Y. and Schondeld S. A., “Mechanism of production of crackles after atelactasis during low-volume breathing”, Am Rev Resp Dis 126:413, 1982; and Forgacs, P., “The functional basis of pulmonary sounds”, Chest 73:399, 1978). These crackles are inspiratory sounds, which may occur when peripheral airways pop open as atelectatic regions are inflated.
With atelectasis due to shallow breathing, the crackles often disappear after a few deep breaths or after changes in the position; whereas with pulmonary fibrosis, the crackles persist. In mild pulmonary fibrosis, a disease that is explored here, the crackles are predominantly heard late in inspiration, but may become pan-inspiratory with an end-inspiratory accentuation as the disease progresses. Late-inspiratory crackles are often repetitive with several respiratory cycles and initially identified in dependent lung zones. Late-inspiratory crackles indicate a loss in lung volume and are audible over the chest walls. Early-inspiratory crackles are scanty, low-pitched and audible at the mouth as well as over the chest.
Although the present invention to be disclosed here can be used to identify any lung disease that produces sounds that can be processed using the apparatus and method of the invention, two particular diseases have been used to demonstrate the effectiveness of the invention and, therefore are discussed in some detail here.
Chronic Bronchitis
This condition produces excessive secretion of mucus, resulting in chronic cough productive of sputum. Pathologically, bronchitis is characterized by proliferation and hyperplasia of the mucus glands in the large airways, extending abnormally into small airways, often without evidence of inflammatory changes, although the changes may be associated with bacterial infection. Chronic bronchitis is commonly caused by the inhalation of cigarette smoke, although the disease is found in a few nonsmokers as well, particularly miners and people living in polluted urban environments. The principal complication associated with chronic bronchitis is the development of obstructive airway disease.
Interstitial Fibrosis
This condition, also called interstitial pneumonitis, is associated with interstitial and alveolar infiltrates and fibrosis. Patients complain of coughing, or difficulty in breathing and, although rarely, of fever. Pulmonary function studies show restriction and are sensitive indicators of the extend of the illness. Interstitial fibrosis may be caused by cancer chemotherapeutic agents (bleomycin, cyclophosphamide, methotrexate), radiation therapy, the antibiotic nitrofurantoine, high oxygen concentrations inhaled over a long period, and heavy metals such as gold. It is most often idiopathic.